Magnetron pulsing control circuit



Jan. 15, 1957 M. G. WHITE 2,777,954

MAGNETRON PULSING CONTROL CIRCUIT- Filed May 7, 1946 HIGH VOLTAGE SOURCE PULSED V14 LIGHT SOURCE INVENTOR MILTON 6. WHITE BY I ATTORNEY United States I Patent D MAGNETRON PULSING CONTROL CIRCUIT Milton G. White, Princeton, N. J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 7, 1946, Serial No. 667,754

2 Claims. (Cl. 250-36) This invention relates to electron discharge devices and more particularly to a photoelectric emission controlled magnetron.

In pulse modulation of a microwave generator such as a conventional magnetron, a modulator is required to form voltage pulses of the proper shape and size for application to the magnetron cathode. In the conventional modulator a high-vacuum triode, a thyratron, or

a spark gap is used as a switching tube. These modulators are subject to certain disadvantages, such as the limitation of the pulse repetition frequency by the deionization time of the switching tube in the thyratron and spark gap type modulators, and the complexity of components and circuitry required in the high vacuum triode type modulators.

The principal object of this invention is to provide an electron discharge device which can be pulsed without the use of conventional pulsing equipment, thus overcoming the above-mentioned disadvantages.

Another object of this invention is to provide a magnetron which can be pulsed at a high repetition rate by photoelectric means.

Still another object of this invention is to provide a magnetron which will perform the function of a switching tube in addition to its primary function of generating electromagnetic oscillations.

Other and further objects will appear in the course of the following description when taken with the accompanying drawing which is a schematic representation of one embodiment of this invention.

In the drawing is shown a magnetron 7 having a cathode 8, an outer envelope 9 comprising the anode in which are formed a plurality of cavities 10 opening onto the space between cathode 8 and anode 9, and an output connection 11 to one of the cavities 10. Magnetron 7 is of the conventional type except for a modification in cathode 8 as hereinafter described, and the addition of a small hole 12 drilled radially through the magnetrons outer envelope. A glass window 13 covering hole 12 maintains the vacuum inside magnetron 7 and yet permits light from an external source 14 to pass through hole 12 and shine on cathode 3. Light source 14 contains a neon or other suitable bulb and provision for supplying electrical energy to the bulb in short rapid pulses so that a pulsed light beam is produced. Cathode 8 is coated with a silver-magnesium alloy or other suitable coating such that electrons may be emitted by photoelectric and secondary emission. There is no provision for heating cathode 8 and thus thermionic emission is negligible. Cathode 8 is insulated from outer envelope 9 of magnetron 7 by a copper-glass seal 15 and is connected to an energy-storage device such as pulse forming network 16. Network 16 comprises a tapped inductance 17 and condensers 18 connected between the taps and ground to form a 1r type network and is connected to a source 19 of high negative potential through resistor 20.

Network 16 is normally charged to the potential of 2 source 19' and this voltage also appears between cathode 8 and anode 9 of'the magnetron, since anode 9 is connected to ground; When light from source 14 strikes cathode. 8, electrons are emitted by photoelectric emission and are attracted toward anode. 9. The conventional magnetron axialmagnetic field present (not shown) is perpendicular to the. electricfield'between cathode 8 and anode 9 and causes these electrons to return to and strike the cathode, thus causing emission of secondary electrons. These secondary electrons follow the same cycle as the electrons resulting from photoelectric emission and cause further secondary emission. This emission process is cumulative and results in the passage of a large current between cathode 8 and anode 9 which is limited by network 16. Current continues to flow until network 16 has been discharged, whereupon the process stops provided that no further light is allowed to reach cathode 8 from source 14. The passage of this electron stream past cavities 10 sets up electromagnetic oscillations in them in the conventional manner so that energy can be taken from output connection 11. In the ensuing interval of time before light source 14 is again turned on, network 16 recharges through resistor 20 to the potential of source 19, and the cycle is ready to be repeated. The rate at which this magnetron can be pulsed is limited only by the maximum allowable average power dissipation of the magnetron and the frequency at which the light beam can be modulated.

This invention is only to be limited by the appended claims.

What is claimed is:

1. An arrangement for pulsing a magnetron of the type in which a constant, unidirectional magnetic field is applied axially through the cavity spaces of the anode block comprising, in combination, a photo-emissive cathode centrally disposed within said anode block with its longitudinal axes parallel to the direction of said magnetic field, a pulse-forming network, a resistor in series therewith, a source of direct current voltage connected to the series combination of said pulse-forming network and said resistor for energizing said network, said network being connected between said cathode and said anode block such that a radial electric field exists between said cathode and said anode block whenever said pulse-forming network is energized, a source of intermittent light external of said anode block, an aperture extending through said block and serving as a light transmission path for directing light radiated from said source upon cathode whereby electrons emitted therefrom in response to such illumination are returned to said cathode under the influence of said magnetic field to produce secondary emission and providing a low impedance conductive path between said cathode and said anode block for deenergizing said network, said network be ing energized from said direct current voltage source during the period of time said light source is off, and means for extracting the oscillatory signal produced by the magnetron in response to its excitation by the deenergization of said network.

2. An arrangement for periodically energizing a magnetron of the eype in which a unidirectional magnetic field is applied axially through the cavity spaces of the anode block comprising, in combination, a photoemissive cathode disposed within the central cavity of said anode block with its longitudinal axis parallel to the di- :rection of said magnetic field, said cathode having secondary electron emissive properties, a pulse-forming network, a resistor in series therewith, a direct current source of potential coupled to the above series com bination for charging said network, said network being coupled to said cathode and said anode block such as to produce within said central cavity a radial electric patent d Jan 15,,,1.9e1.

nating in an inductive loop coupled to one of the cavity spaces of said anode block for extracting the oscillatory signal produced by the excitation of said magnetron in response to the sudden discharge of said pulseforming network.

References Cited in the file of this patent UNITED STATES PATENTS Hansell Oct. 8, 1946 Hansell Nov. 5, 1946 

